Warn users about using `bin/accountadmin` for first time setup

Summary: The "easy setup" is sort of an exaggeration since it basically just amounts to getting you logged in correctly, but it will probably be more true in the future.

Test Plan: Ran `bin/accountadmin` with zero and more than zero accounts.

Reviewers: asherkin, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7678
Handle "-p port" flag in ssh-connect

Summary:
The documentation is explicit that Git does not pass this flag:

  The $GIT_SSH command will be given exactly two arguments: the username@host (or just host) from the URL and the shell command to execute on that remote system.

This isn't true; it does. Accommodate it.

I'll see if I can fix this in the upstream, too.

Test Plan: Ran various `ssh-connect` commands with -p, etc.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7680